The goal of the proposed research is to understand some of the fundamental properties of mammalian presynaptic nerve terminals. Pinched-off nerve endings (synaptosomes) isolated from rat brain will be used, because they retain many functional, metabolic, and morphological properties of intact neuronal tissue, and are well-suited for studies that involve radiotracer-flux, optical, and biochemical techniques. The Investigator will: 1) examine the characteristics of the presynaptic Ca channels involved in neurosecretion - permeability and selectivity, and mechanism of inactivation; 2) determine how cations that permeate, and selectively block, Ca channels influence Ca sequestration and extrusion and transmitter release; 3) measure intracellular pH in the nerve terminals, study how it is regulated, and how it is related to Ca channel activity and neurosecretion; 4) develop and utilize methods for loading Ca-indicators into nerve terminals, so that Ca metabolism and its relation to the activity of nerve terminals can be investigated. This project will provide a better understanding of the basic cellular mechanisms that control intracellular Ca and pH in brain nerve endings, and of how this regulation affects the relase of brain neurotransmitters.